Compact pumps of this type are equipped with a diaphragm assembly including plural diaphragm units which form plural respective pump chambers in a case, and perform a pumping operation in such a manner that a bottom end portion of each diaphragm unit is moved in the top-bottom direction by a swing body that is swung by an eccentric rotary shaft. Compact pumps of this type take in and exhaust (discharge) air as an intake valve element and an exhaust valve element operate in link with the movement, in the top-bottom direction, of the bottom end portion of each diaphragm unit.
Such compact pumps are called diaphragm pumps because of the use of the diaphragm assembly. The diaphragm assembly is also called a diaphragm collection or a diaphragm main body. Each intake valve element is also called a suction valve or a suction valve element. Each exhaust valve element is also called a discharge valve or a discharge valve element. The swing body and the eccentric rotary shaft are also called a drive body and a drive shaft, respectively.
In such compact pumps, the intake valve elements (suction valves, suction valve elements) and the exhaust valve elements (discharge valves, discharge valve elements) perform opening/closing operations as air is taken in and exhausted (discharged). As a result, operating sounds are generated when these valve elements (valves) perform opening/closing operations. This results in a problem that the operating sounds leak to outside the case to become noise (noise sounds). Likewise, intake sounds (suction sounds) are generated when air is sucked into the case from outside the case. This results in another problem that the intake sounds leak to outside the case to become noise (noise sounds).
To solve the above problems, various techniques for preventing (suppressing) of noise (noise sounds) have been proposed conventionally.    Patent document 1: JP 2003-269337 A    Patent document 2: JP 4,306,097 B    Patent document 3: JP 2012-241636 A
For example, Patent document 1 discloses a diaphragm pump in which noise sounds that are generated when suction valves are opened and closed are suppressed. In the diaphragm pump disclosed in Patent document 1, suction valves are provided in a flat-plate-shaped portion to which diaphragm units of a diaphragm main body are connected. Each suction valve has a thin valve portion and an opening that is formed, for example, around the valve portion. In each suction valve, the surface, located on the side where a suction hole is formed on a cylinder, of the valve portion has a concave portion. In the diaphragm pump disclosed in Patent document 1, a discharge valve is disposed approximately at the center of the plural diaphragm units. A discharge outlet is disposed over the discharge valve.
In the diaphragm pump disclosed in Patent document 1, only a portion, around the concave portion, of each suction valve comes into contact with the surface of the cylinder, whereby the generation of noise sounds can be suppressed.
Patent document 2 discloses a compact pump in which noise generated by intake valve elements is weakened. In the compact pump disclosed in Patent document 2, each diaphragm has a through-hole in its bottom portion at the center. A swing body has air introduction holes which communicate with the respective through-holes. Each intake valve element is formed by cutting away a part of the diaphragm. An intake valve portion is formed by the intake valve element and the through-hole which are formed in the bottom portion of each diaphragm. A case upper plate has one exhaust hole at the center. The case upper plate has, around the exhaust hole, plural ring-shaped recesses which communicate with the exhaust hole. Each exhaust valve element is inserted in the associated ring-shaped recess and the exhaust hole. The exhaust valve elements are top end portions of the diaphragms, respectively, and are have a cylindrical shape. Exhaust valve portions are formed in such a manner that the exhaust valve elements are brought into pressure contact with inner wall surfaces that define the ring-shaped recesses and a wall surface that define the exhaust hole, respectively.
In the compact pump disclosed in Patent document 2, since the intake valve elements are housed in the case completely, operating sounds of the intake valve elements are muffled in the case and noise decreases that leaks to outside the case.
Patent document 3 discloses a diaphragm pump in which noise sounds that originate from suction sounds are weakened. In the diaphragm pump disclosed in Patent document 3, a diaphragm holder which holds a diaphragm is provided with muffling chambers. Fluid that has been sucked through a suction inlet flows into a muffling chamber, passes through another muffling chamber, and flows into a pump chamber via a suction hole. When the pump chamber is contracted thereafter, the fluid is pushed out of the pump chamber, flows through one discharge hole, and supplied to a pressurization target from a discharge outlet. In the diaphragm pump disclosed in Patent document 3, one discharge valve element is disposed approximately at the center of plural diaphragm units. The discharge outlet is disposed over the discharge valve element.
In the diaphragm pump disclosed in Patent document 3, noise sounds originating from suction sounds can be weakened because fluid that has flown into the diaphragm pump is guided to a muffling chamber immediately.